1. Field of the Invention
This invention is in the field of above ground clutter canceling for use with Synthetic Aperture Radar imaging.
2. Description of the Related Art
Synthetic Aperture Radar (SAR) radar is used for ground mapping as well as target identification. The general principle behind SAR is to coherently combine the amplitude and phase information of radar returns from a plurality of sequentially transmitted pulses from a relatively small antenna on a moving platform.
The plurality of returns creating a SAR image generated by the transmitted pulses along a known path of the platform make up a frame length. During the frame length, amplitude as well as phase information returned from each of the pulses, for each of many range bins, is preserved. The SAR image is formed from the coherent combination of the amplitude and phase of return(s) within each range bin, motion compensated for spatial displacement of the moving platform during the acquisition of the returns for the duration of the frame length.
The plurality of pulses transmitted during an SAR frame length, when coherently combined and processed, result in image quality comparable to a longer antenna, corresponding approximately to the “length” traveled by the antenna during the frame length.
However, where ground targets of interest are under a forest canopy or some other vegetative cover, the SAR imaging may not reliably detect the targets. In the prior at, lower operating frequencies (VHF and UHF) have been used to penetrate forest canopies. This is because VHF and UHF frequencies have lower attenuation through forest canopies or other vegetative cover, while still providing a radar return from metal, reflecting targets. However, this VHF and UHF approach failed in many instances.